The present invention relates to a wear-resisting attachment for protecting metallic members, particularly the blades of fans or turbines, against erosion caused by air-borne abrasive particles carried by a substantially linear air flow, to which such members are exposed.
By installation of axial flow fans in places, where considerable amounts of particles of abrasive materials are carried by the air volume conveyed by the fan, such as in the case of induced draught fans for coal-fired boilers in power stations, where the flow of flue gas passing the fan blades may have a great content of air-borne ash particles, the fan blades are exposed on the surface portion facing the air flow, i.e. particularly the leading edge, to a heavy wear in the form of erosion of the blade material.
This erosion is caused by the energy conversion taking place when ash particles impact on the blades and, at high loads, it may result in a very short lifetime for the blades.
In practice, it has been shown that the important parameters for the progress of the erosion beyond the characteristics of the blade material are the velocity, the impact angle, the hardness and the magnitude of the particles. In addition thereto, the progress of the erosion may in some cases be accelerated by chemical- or temperature-related influences. Thus, the presence of aggressive gases in the air-flow may at small energy conversions result in an accelerated wear which for some materials, such as rubber and plastics, may also arise at high temperatures.
It is known to provide fan blades for such applications where the blade material may be stainless steel with a wear-resisting attachment of a very hard material, such as hard chromium. In practice, however, local penetrative abrasions of such wear-resisting attachments have appeared to occur at, or symmetrically around the extremity of the leading edge of the blade, whereas the attachment outside these local penetrative abrasions may be relatively intact.
In practice, these problems have particularly been recognized for fan blades. However, it must be assumed that they will also apply to other metallic members, including particularly turbine blades which are exposed to a mainly linear air-flow carrying a considerable content of abrasive particles.